Aperture coupled patch antennae are known for use in receiving and transmitting high frequency signals such as microwave signals. These are particularly suitable for mobile satellite communications and are applicable to communication systems in mobile vehicles. An example of such a patch antenna is shown in U.S. Pat. No. 5,043,738. Our EP Application 93307667.1 also shows an aperture coupled patch antenna for use with a mobile vehicle. In that case the automotive glass is shown as the dielectric between the patch and the ground plane. Problems can arise with environmental protection when the patch is provided on an exterior surface of a vehicle glazing panel. Furthermore problems may arise in achieving satisfactory dielectric properties between the patch and the ground plane depending on the thickness of glass used. Furthermore, if the antenna dielectric is laminated glass and the plastics interlayer is included between the patch and the ground plane then further losses may arise. It is also desirable that the antenna should be capable of transmitting high quality circular polarised radiation thereby giving improved operation in a global positioning system where the vehicle may be required to travel in any direction. In the above mentioned EP Application 93307667.1, two feed lines for the antenna are arranged to be insulated at their cross-over point in order to achieve high quality circular polarisation.
It is an object of the present invention to provide an improved antenna wherein some embodiments have an improved feed system for achieving high quality circular polarised radiation.
It is a further object of the invention to provide some embodiments in which the dielectric properties between the patch and the ground plane can be carefully controlled to provide high quality performance without such dependence on the glass used in the vehicle glazing panel.
It is a further object of the invention to provide some embodiments in which the patch may be protected by location on an internal surface of a vehicle glazing panel.
It is a further object of the invention to provide some embodiments in which the antenna is formed as an assembly which may be attached to an internal surface of a vehicle glazing panel after formation of the glazing panel.